We have shown previously that stimulation of human monocytes with mAB to CD45 induces the production of M-CSF which is strongly augmented by IL- 1beta. To determine at what molecular level IL-1~ augments M-CSF expression we investigated the transcriptional rate and the half-life of anti-CD45 induced M-CSF message in cells stimulated in the presence and absence of IL-1beta. Although the initial steady-state M-CSF mRNA levels in anti- CD45/IL-1beta treated cells were higher compared to those in cells treated with anti-CD45 alone, IL-1beta had no effect on the M-CSF message half- life. Nuclear run-on assays demonstrated that IL-1beta enhanced M-CSF transcript levels through transcriptional mechanisms. The IL-1beta-induced enhancement of M-CSF message levels depended on de novo protein synthesis and M-CSF secretion induced by IL-1beta could be blocked by soluble IL-1 receptors. Both, IL-4 and IL-10 strongly inhibited M-CSF production by human monocytes stimulated with anti-CD45/IL-1beta which was accompanied by decreased M-CSF message levels. Nuclear run-on assays demonstrated that IL- 4 and IL-10 decreased M-CSF message levels by repressing M-CSF gene transcription whereas M-CSF message half-life was not affected. These data have been submitted for publication. In a related project we are studying the effect of HIV-1 infection on M-CSF production by human monocytes. In a separate study we are currently investigating signal transduction through the c-fms receptor by stimulating human monocytes and monocytic cell lines with M-CSF followed by immunoprecipitation with anti-phosphotyrosine antibodies and western blotting. We can detect three proteins with molecular weights of 56 kd, 95 kd and 120 kd phosphorylated on tyrosines residues. Studies are underway to identify these proteins and their relationship to c-fms.